Central CRD server

I have a number of asterisk systems installed and one of the problems I have is keeping track of individual user costs.
I would like to send all of the CDR logs from each servers, over the Internet, to one central server where we could generate usage statistics. I’ve been looking on the net but since I’ve not done this before, have been having a hard time finding information.
Is what I am looking for called a mediation server for example? And is there an open source server out there which could do the job?

Thanks very much.